A hemodialysis treatment is used for treating patients who have acute or chronic renal insufficiency. Blood is taken from the patient in an extracorporeal blood circuit and passes through a dialyser which removes uremic toxins in the blood and reconstitutes the blood by balancing electrolytes, such as sodium, potassium, calcium and magnesium, and adding necessary substances, such as bicarbonate. Moreover, a certain amount of fluid is removed from the blood , called ultrafiltrate, since the patient cannot expel superfluous fluids in the normal manner. Hemodialysis primarily uses diffusion through a semipermeable membrane in order to perform this treatment.
Another treatment procedure which has been used more often recently is hemofiltration, whereby the blood is filtered in a hemofilter and the filtrate is discarded. Substitution fluid is then added, either before or after the filtration, for replacing the discarded ultrafiltration fluid. Hemofiltration primarily uses convection for removing the uremic toxins, and the substitution fluid comprises the necessary electrolytes for balancing and fluid addition purpose. A smaller amount of substitution fluid is added compared to the amount of ultrafiltrate fluid which is removed, in order to remove the necessary amount of fluid from the patient.
Another treatment procedure utilized is a combination of hemodialysis and hemofiltration, and is called hemodiafiltration. This procedure is essentially a combination of these two treatment procedures, and uses a hemodiafilter.
These treatment methods are described in numerous text books and it is not necessary to describe them in more detail in the present specification. One description is in the chapter: "Hemodialysis Machines and Monitors" by Polaschegg H D, Levin N W in "Replacement of renal function by dialysis", by Jacobs C, Kjellstrand C M, Koch K M, Winchester J F, 4th ed. Kluwer academic publishers, 1996:333-79.
The above-mentioned substitution fluid can be prepared as a pharmaceutical solution. However, doing so is expensive. Therefore, it is preferred to produce the substitution solution on-line in connection with the dialysis machine, by filtration of the dialysis fluid. However, a preparation method must be devised and adapted for preparing a substitution fluid that is sterile and can be used for infusion purpose.
Thus, a dialysis machine which is adapted for hemofiltration and hemodiafiltration also includes a device for preparing the substitution fluid on-line. This device usually comprises two filters for producing the substitution fluid and for securing the sterility of the prepared fluid.
Some patent specifications describing devices of interest for accomplishing these goals are U.S. Pat. No. 4,209,391, assigned to Cordis Dow; European Patent No. 189,561, assigned to Fresenius; German Patent No. 3,448,262, assigned to Fresenius; U.S. Pat. No. 4,834,888, assigned to Fresenius; European Patent No. 407,737, assigned to Fresenius; German Patent No. 4,240,681, assigned to Fresenius; European Patent No. 692,268, assigned to Fresenius; European Patent No. 165,519, assigned to Gambro; European Patent No. 694,312, assigned to Hospal; and European Patent No. 745,213, assigned to Gambro.
Previous dialysis machines for producing on-line substitution solutions comprise a peristaltic pump arranged upstream of the dialysis machine for propelling the substitution fluid. A peristaltic pump comprises several rollers interacting with a plastic tube pump segment and occluding the pump segment. By moving the roller along the tube while occluding the tube, the fluid is pumped. The substitution fluid flow rate is thus approximately proportional to the rotational speed of the peristaltic pump.
The peristaltic pump is used since it can easily be placed on the front of the machine, and because it cooperates with a tube portion that can be produced as a sterile article. However, the tube portion so utilized has a limited life time. Thus, the pump segment and the second filter must be replaced, for example after one month, which creates comparatively high costs. Also, the peristaltic pump involves added costs, and uses a relatively large additional space on the front of the machine. The peristaltic pump is thus placed on the front since the pump segment must be replaced regularly. All this makes preparation for the treatment complicated.
If the peristaltic pump is used with a disposable tube system and a disposable second filter, the disposable tube system must comprise a pump segment and the second filter. Thus, such a disposable tube system is comparatively expensive and bulky.
The object of the present invention is therefore to provide a method and apparatus which obviates the drawbacks of the prior art dialysis machines.
Another object of the present invention is to provide a dialysis machine for producing substitution fluid on-line, in which the peristaltic pump previously used is dispensed with.